It is frequently necessary to join two metal strips together at the intake of a strip-treatment plant, that is a rolling mill, so that the mill can operate continuously and so that it is not necessary to rethread the strip through the mill each time a new strip is being processed. More particularly, coiled strips are generally unwound at the intake, then run through one or more processing stations, and at the outlet are optionally wound up again or alternatively also cut into plates. This way, the leading end of a new coil is spliced to the trailing end of the last coil so that the strips do not always have to be rethreaded. In this context it is known from practice to splice the metal strips to one another by welded joints.
With different types of metal strip and in particular metal strips of aluminum alloys, welded joints often cause problems in practice. For example, resistance spot welding with aluminum alloys causes the problem of spattering. Furthermore, there is the danger of the electrode adhering to the strip and minimum spacings between two adjacent spot welds are necessary due to the electrical connections. Some alloys cannot be welded at all by means of resistance spot welding. The same applies to resistance seam welding that likewise has the problem of spatter formation with aluminum alloys and otherwise has a low seam quality. Poor seam qualities also result with friction stir welding, in particular with small strip thicknesses.
For this reason, punched joints, also referred to as stitching, were also used as an alternative to welding and as a rule can be used up to a strip thickness of approximately 6 mm. The problem thereby is often the fact that in the course of punching burrs caused by the cutting gap of the two punching tools or chip particles that are loose or are still slightly spliced with the strips are produced. When the strips pass through a strip-processing line and run around processing line rollers in this joint, the burrs or chips can break off and adhere to the processing line rollers, particularly if these rollers are plastic-coated. In order to prevent this, it is basically known to adhere punched joints by means of adhesive tape (see for example US 2007/0029039). Otherwise, adhesive joints are also used in practice, but as a rule only up to a strip thickness of no more than 1 mm. In the case of greater strip thicknesses there is a danger that the adhesive seam will be sheared open in the strip-processing line while running around rollers due to the bending stiffness of the strips.
Finally, a spot-welding head for a strapping machine is known from U.S. Pat. No. 5,880,424, where in a strapping machine of this type, for example a steel strip coil, a wire coil, a group of pipes or rods or bars or a stack of plates is strapped with a steel strip. The overlapping sections of a steel strip of this type can be spliced to one another by means of spot welding.